A hard disk drive includes a disk on which data is stored, a spindle motor which rotates the disk, a read/write head, and a voice coil motor (VCM) to move the head over the disk for reading/writing from/to the disk surface. When the disk is not rotating, the VCM moves the head away from the disk area. When the disk is rotating, and read/write operations are in progress, the head, which is carried on a VCM arm, is positioned above the data storage surface of the disk. When the disk is not rotating, the head is moved away from the disk in order to prevent any damage to the disk. When power loss (any power supply inactivation such as a power failure event or a power-down event) occurs, the disk will slow down and eventually stop due to its inertia. Whether the power loss is due to a power failure or a power-down event, there are several known ways to obtain energy for moving the head to a safety zone away from the disk. This movement of the head to a safety zone is also often referred to as “parking the VCM arm”.
One conventional source of energy for retracting the read/write head away from the disk is the spindle motor, which generates energy as it slows down but nevertheless continues to rotate for a period of time. This is illustrated in FIG. 1. The voltage VM generated by the slowing-down spindle motor produces a current 11 that passes through the VCM 13, to effect retraction of the read/write head.
Another known source of energy for retracting the read/write head is a storage capacitor C0 connected as shown in FIG. 2. Energy is stored in the capacitor C0 while the power supply is present during normal operation, and this stored energy is used to retract the read/write head after a power loss event. In particular, the capacitor voltage VM2 produces a current 21 which passes through the VCM 13 to effect retraction of the read/write head.
Another known scheme uses a capacitor in combination with a boost circuit such as shown in FIG. 3. The boost circuit 30, for example a charge pump, operates to boost the capacitor voltage to a level that is higher than the nominal power supply voltage VCC. As shown in FIG. 3, the boosted voltage arrangement requires an additional switching device, namely FET M11, for directing through the VCM 13 a current 31 produced by the boosted capacitor voltage VBOOST.
In any of the prior art approaches of FIGS. 1–3, the amount of energy available for moving the read/write head after a power loss event is limited. Accordingly, the present invention recognizes that the effectiveness of the power loss head retraction scheme depends on how efficiently the retraction energy source is utilized. That is, in order to provide for a reliably effective power loss retraction operation, the retraction energy source must be used efficiently.
It is therefore desirable to provide for a power loss head retraction architecture which uses the available retraction energy source more efficiently than the prior art approaches.